Device for the magnetic recording on, and reproducing from, diskshaped sound carriers



2, 1950 w MULLER EI'AL 2,519,

DEVICE FOR THE MAGNETIC RECORDING ON, AND REPRODUCING FROM, DISK SHAPEDSOUND CARRIERS Filed Feb. 27, 194B 2 Sheets-Sheet 1 Fig .1

Aug. 22, 1950 Filed Feb. 27, 1948 wJ MULLER ElAL DEVICE FOR THE MAGNETICRECORDING ON, AND REPRODUCING FROM, DISK SHAPED SOUND CARRIERS 2Sheets-Sheet 2 Patented Aug. 22, 1950 2,519,592

ZNIIIZED *ijfISiT-ATYES SPATENT {.ZO-EFICE Mnacht, Switzerland,assignors to Daphns Investmenj; Trust," Vaduz, Liechtenstein-Afiplication =February 2731948;;.Serial Nos-1113814 2 ImSwitzerlamdDecembrf ZS; 1947 3'Claims. l izfilherinventionr'relates to anprocessand to'an znapparatuszfornthe magnetic -recording and: re roducingaof-zsound:- ondand from" vdisc shaped oundz:.carriers,---rrespectively.

mincreasingtthe recording capacity of a'disc shaped oundvcarrier.

:EDHillhElIGOJ OIlGUhdS? been compelled to use :pick- Youptcores zof:.2c;;millimeter: pole width or:- more in 2 order tozobtain a sufficientreproductiontvoltagem Sinote'pnevmustnotago-below a certainminimumistancesof athewrecorded soundtracks from oneTIQthGIZIthGzIECOIYdi-DQ6311132011337 for a given sound frequencyofirspeech was-:determinedcthereby.

sInrorder aneverthelesssto achieve a; greaterre-s.

millimetergzorrless for recording and" reproducing. MWithasdiscishapedwsound' carrier; a- -pich upv of halfcthezpole-widthaallowstheoretically-to record i -On asispirali track oful'lalfithe-spiralangle whereby twic the mimbefof turns "andaccordingly twice.

' the recording capacity-on one and the same" side of the disc is'attained.

tof oodrse abylathe narrowing of the pole width of the pick-up thereproduction voltage is diminished proportionally to the pole width. Inorder nevertheless-to'achieverecording and/orreprorisvrducingsthatzsatisfies: 'all requirementsaccording to anotherfacture of the inventiongtwo pickups are putwintooperationsimultaneously on the upper. and lower side of the soundcarrier. As: 45

.Wiflb seen, the recording" capacity of ea'ch intdividual -si'deofthedisc is doubled thereby',' while 'that"ofthe"disc"as 'a'wholeremains substantially the same. But the essential advantage is achievedthat any switching-over from one side to the other can be dispensedwith.

The idea of operating simultaneously with two pick-ups allows moreoverto improve the quality of the recording and reproduced sound,particularly with large discs of e. g. 300 millimeters:Iherinventionuhasfithe object of substantially:

jacentezsoundrtracksi fromr oneanother-i of-r 205,;

diameter. When, using it such plates the circumferential velocityrelatively.-tathepiek-ups varies a, on their path across v..the..radiusfofsthemdisc. If a-l-twospick-lupssarearranged in series and a. areamounted, according .-.to, a rfurther. feature lofI the .invention ona.. commondork shaped ,carrier in nsuchr a manner that theionelpickeupisrat the .-.beginning.= of i record-ing...or reproducing atw'the innerend of its associatedsoundtrack -andthe l0. other -pick-up is .atstherouter .zendl of Hits. corresponding sound track; rwhereafter they.move.op-

positely i. eithehone from; inside: outwardssa'nd lathe other. outsideinwards, the different circum- H.ferentialwelocitiesi oiithe soundcarrier disc with lfin-respectsto; the pick-ups have the efiect that theouter pick-up =records; and/ or reproduces at. the highercircumferentialsvelocity.mainly .theah-igh sound frequencies,.andnthesinner --picl-:- .up..at. the lower velocity mainly the lowersound-frequeni=cies.-;-Since at reproductionmthe svoltages-lproducedbysthe two pickeupssupplement one another, one attainsinithis manner animproved and constant quality ofmsoundreproduction.

Itis wellnknownuthat hitherto variable speed25.,drivaaggregateswererequired for sound carrier ..discs,the soundtracksof which would otherwise shave... had varying..cirt-zuinferential-v velocities, in worderv. :tofattain a constant 7quality .of reproducmtion.

lhe inventive ideauassset forthhereabove will -=:-.'nowbeascertainedwith: reference to .the accomanying drawings whichv show.diagrammatically -ml'i-ow-iand-by meanstof :what kind of device it.can

for-example hesperformedsin. practice.

Fig; 1 is ardiagrammaticfi elevation, partly. in e section of anapparatus forsmagnetically record- "ningrsound on; or-reproducingitfrom-,- amdisc .a shaped-carrier. Fig. 1a is anplansview asseen.11from-belowyandiig. 1b is a diagrammatic .part

40:;secti'on on alarger scale.

v'Figs; 2-to 4*arerdiagrammatic: plan viewsson a ;smaller scale invarious positions of theflpickrups 1 with respect :to the sound carrier.

Iii-the drawing, lndenotes-thedisc shaped-sound ...arrier which isrotatablyrarrangedionilthepin 3 ozfixedrtowthe plate 2. Thesplate I is.connected, pier example byrrneans'i of rivets: I (L -to the zflange.ssof a hub lltiwhichhas aeworm'wheel Hw (Hg-11a) in mesh with a wormtzoon laispindle' l 3 'driven by the electric motor l4. Said spindlecarries another worm H5 in mesh with a worm wheel segment !6 pivoted onan axis 8. Two picks-ups i, 5 (Fig. 1b) are arranged, the one top of theother below the disc I. These picks-ups are arranged on the rigidlyconnected arms 6, 1 that form together a fork-shaped carrier and are, asa whole, pivoted about the said axis 8 and connected with the segment18. The pole gap of the two pick-ups (which cause longitudinalmagnetisation of the sound track) is only about half of that of theusual single pick-up that would produce the same voltage of reproductionas the two pick-ups according to the invention together, and amounts to.2 millimeter or less, the distance of adjacent sound tracks being .05millimeter or less. With a frequency of speech of about 3000 hekacyclesper second and a disc diameter of 300 millimeters a recording periodand/or reproducing period of about 30 minutes was attained.

As will be seen from the plan views in Figs. 2 to 4 the two arms 6, Iwhich are rigidly connected with one another, include an angle and areoff-set vertically to one another as will be seen from Fig. 1, so thatthe sound carrier can find room between the two arms 6, l and associatedpick-ups 4, 5.

As will be clear without saying, the circumferential velocity of thesound carrier disc I will be much higher at the outer pick-up than atthe inner pick-up (Fig. 2). In the course of record ing thecircumferential velocities at the pickups vary, since the one (4) movesinwards and the other (5) outwards.

A position (Fig. 3) will be reached in the process at which the twopick-ups stand at the same diameter. Upon the further continuation ofthe movement of the arms 6, l the circumferential velocity at thepick-up l diminishes further,

while that of pick-up 5 increases further. At the end of the movement(Fig. 4) the velocity conditions are just reversed as compared with thebeginning of the recording and/or reproducing (Fig. 2).

The off-set arrangement of the pick-ups gives the advantages asinitially mentioned.

What we claim as our invention and desire to secure by Letters Patent,is:

1. In a device for magnetically recording or reproducing sound, amagnetizable rotary record disc, a pair of electromagnetic pick-upsconnected in the same telephonic circuit and arranged to act uponopposite faces of said record disc, and a bell-crank lever, means forpivotally supporting said bell-crank lever about an axis extendingparallel to the axis of rotation of said record disc, said means beingarranged outside the circumference of said disc, one arm of saidbell-crank lever extending above the upper face of said record disc andthe other arm extending below the lower face of said record disc, saidpick-ups being secured to the free ends of said arms of said bell-cranklever in a position to be moved across the upper and lower facesrespectively, of said record disc upon pivoted movement of saidbell-crank lever, the angle formed between the arms of said bell-cranklever and the distance of said pivot means from the axis of rotationbeing of said record disc such that upon pivotal movement of saidbell-crank lever one of said pick-ups is moved in a direction toward thecenter of said record disc while the other pick-up is moved in adirection away from the center of said record disc.

2. In a device for magnetically recording or reproducing sound, amagnetizable rotary record disc, a pair of electromagnetic pick-upsconnected in the same telephonic circuit and arranged to act uponopposite faces of said record disc, a bell-crank lever, means forpivotally supporting said bell-crank lever about an axis extendingparallel to the axis of rotation of said record disc, and said meansbeing arranged outside the circumference of said disc, one arm of saidbell-crank lever extending above the upper face of said record disc andthe other arm extending below the lower face of said record disc, saidpick-ups being secured to the free ends of said arms of said bell-cranklever in a position to be moved across the upper and lower facesrespectively, of said record disc upon pivoted movement of saidbell-crank lever, the angle formed between the arms of said bell-cranklever the distance of said pivot means from the axis of rotation of saidrecord disc being such that upon pivotal movement of said bell-cranklever one of said pick-ups is moved in a direction toward the center ofsaid record disc while the other pick-up is moved in a direction awayfrom the center of said record disc, and means for rotating said rotarydisc and pivotally moving said bell crank lever in such a speed relationto each other that the adjacent sound tracks formed on said record discare spaced from each other a. distance which does not exceed .05millimeter.

3. In a device for magnetically recording or reproducing sound, amagnetizable rotary record disc, means for rotating said disc, abell-crank lever, means for pivotally supporting said bellcrank leverabout an axis outside the circumference of said disc and parallel to theaxis of rotation of said disc, the arms of said bell-crank leverextending with their free ends toward said record disc, one arm of saidbell-crank lever being arranged on one side of said disc and the otherarm on the other side of said disc, and two electromagnetic pick-upseach arranged on the free end of the arms of the bell-crank lever so asto be in operative juxtaposition each with one side of said record disc,one pick-up being positioned near the circumference and the other nearthe center of said record disc in one end position of said bell-cranklever, means for moving said bell-crank lever about .its pivot whereblysaid pick-ups being moved across the upper and lower faces respectivelyof said record disc into the other end position of said bell-crank leverin which the formerly outer pick-up is near the center and the formerlyinner pick-up is near the circumference of said record disc.

WILLY MiiLiER. OSKAR GRIMM.

REFERENCES CITED The following references are of record'in the file ofthis patent:

UNITED STATES PATENTS Stuart Oct. 12, 1909

